The sulphonylureas are a family of drugs based on a common sulphonylurea core. These drugs act via augmentation of secretion of insulin from pancreatic beta-cells. Sulphonylureas may also cause a reduction in serum glucagon and potentiate the action of insulin at the extrapancreatic tissues.

They vary in potency tremendously with first generation sulphonylureas such (e.g. tolbumatide, chlorpropamide) being less potent thant second generation sulphonylureas (e.g. glipizide, glimepiride). Sulphonylureas are metabolised by the liver to less active metabolites which are subsequently excreted by the kidneys. Care should therefore be taken in both renal and hepatic impairment. The duration of action and dosage frequencies of the some commonly used sulphonylureas are shown below:

• tolbutamide - duration of action 6 to 10 hours; dose bd to tds
• chlorpropamide - duration of action 24 to 72 hours; dose od
• gliclazide - duration of action 12 to 18 hours; dose od to bd
• glibenclamide - duration of action 12 to 16 hours; dose od
• glipizide - duration of action 6 to 10 hours; dose od to bd
• glimepiride - duration of action 12-24 hours; dose od

Cautions include:

• sulphonylureas can cause weight gain
• caution is needed in the elderly and in those with mild to moderate hepatic and renal impairment - this is because of the risk of hypoglycaemia
  • short-acting tolbutamide may be used in renal impairment (as may gliquidone and gliclazide) - these are principally metabolised in the liver
  • essential to undertake careful monitoring of blood-glucose concentration
  • important to use the smallest possible dose that produces satisfactory glycaemic control

Side Effects include:

• side effects are generally mild and infrequent e.g. nausea, vomiting, constipation, diarrhoea
• disturbances in liver function may occur with use of sulphonylureas - this may rarely lead to cholestatic jaundice, hepatitis and hepatic failure
• hypersensitivity reactions can occur:
  • generally occur in the first 6–8 weeks of therapy
  • consist mainly of allergic skin reactions - rarely there may be progression to erythema multiforme and exfoliative dermatitis, fever and jaundice
  • photosensitivity - this rare side effect has been reported with chlorpropamide and glipizide
• haematological disorders associated with sulphonylureas are rare - possible adverse effects include leucopenia, thrombocytopenia, agranulocytosis, haemolytic anaemia, pancytopenia and aplastic anaemia
• chlorpropamide is associated with more side-effects than other sulphonylureas, principally because of its very prolonged duration of action and the consequent hazard of hypoglycaemia and it should no longer be used (1)
  • may also cause facial flushing after drinking alcohol (may occur in about 1/3 of patients) - this effect does not generally occur with other sulphonylureas
  • chlorpropamide may also increase secretion of antidiuretic hormone and very rarely cause hyponatraemia (hyponatraemia is also reported with glimepiride and glipizide)

The summary of product characteristics must be consulted before prescribing one of this class of drugs.

Reference:

1. BNF 6.1.2.1